[hpsdr] (no subject)

[Chris Stratton]

>>> The standard MDS measurement is to a 10
>>> dB SNR, 

>Is this correct? I have always seen MDS quoted as a 
> signal power equal 
>to the noise power in a stated bandwidth, so that
>(S+N)/N = 3dB.

>I have never seen the 10db SNR used, at least not in
>weak-signal discussions.

You may be right about that.  At any rate, I think
that the unbelievable claims become merely average
when you go through and figure out what they are
actually measurements of.  

In terms of practical impact, you may be able to
clearly "discern" a signal that is 0 dB above the
noise on the screen of an analyzer that integrates for
30 seconds to make a picture, but you probably won't
be able to copy it by ear in real time.  The reason we
have narrow CW filters is to limit the bandwidth over
which we have to integrate noise power, but within
that bandwidth we can't get better than the integral
of the -174 dBm/Hz thermal noise plus the receiver
noise figure (12-15 dB).  Integrating over 500 Hz adds
27 dB...

Flipping things around, it looks like Cornell Drentea
may well misunderstand the language of the claims of
various SDR projects (especially the QSD designs,
which aren't always intuitive to RF people), much as
SDR people have been initially confused by what he
claims.  



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